The invention relates to a layer system that filters sun and heat and can be applied to glass by means of a vacuum coating process. Said system comprises at least one series of metal layers in addition to a respective series of lower dielectric layers that are positioned directly below said assembly and a respective series of upper dielectric layers that are positioned directly above said assembly as well as a method for producing the same in which the individual layers can be applied successively to a glass substrate by means of vacuum coating.
Such layer systems applied to glass by means of vacuum coating are mainly used in architecture for window and facade design and in the automobile industry. In both areas of application, the layer systems must be chemically resistant and mechanically durable. There are standardised tests for the comparable evaluation of these characteristics such as boiling in 5% hydrochloric acid and various friction tests.
At the same time, the layer systems must exhibit a high level of permeability for visible light (transmission)—transmission levels of approx. 75% to 80% are preferred—and a high level of reflectivity for radiation in the wavelength range of a few μm—the so-called near infrared range. These special wavelength-dependent transmission and reflection properties characterise the layer systems that are primarily used for filtering sun and heat, the known solar management (also solar control) systems. However, in special applications, a high level of reflectivity in the infrared range is also required, which is reflected in the emission behaviour of the layer system.
A further important characteristic of this sun-filtering layer system applied to glass is the possibility it offers for thermal treatment as it is, for example, used in tempering for the manufacture of safety glass for architecture and the automobile industry or for shaping glass for windscreens. As it is necessary in various applications to carry out the coating before thermal treatment for the cost-effective manufacture and attainment of homogenous layers, the layer systems must show mechanical, chemical and optical characteristics that will not worsen or significantly worsen with the various thermal treatments with different temperature and time regimes according to application.
In U.S. Pat. No. 6,159,607, a layer system was described that for the most part meets these requirements. According to this, a metal layer of nickel or a nickel alloy that shows the required reflection characteristics for infrared rays is covered by a stochiometric silicon nitride layer (Si3N4) that in turn makes the layer system mechanically and chemically durable.
The metal layer containing nickel shows no decrease in emission property following thermal treatment. However, it has been shown that in the course of heat treatment, diffusion processes, in particular of the nitrogen from the silicon nitride into the metal layer and of the nickel in the reverse direction, occur.
As a result of this process, depending on the temperature and length of thermal treatment, colour displacements may occur compared to non-thermally treated coating systems, which is particularly undesirable for use in architecture. For instance, in facade planning, for cost reasons, thermally treated safety glass is only used where it is actually necessary for avoiding accidents so that non-thermally treated and thermally treated glass is always used together and any colour differences are therefore particularly apparent.
As such colour differences are also undesirable for infrared-reflective layer systems in the further infrared range with wavelengths of approximately 10 μm, an anti-migration layer, preferably containing nickel chromium oxide, was inserted in such a layer system described in WO 02/092527 between the reflection layer and a dielectric layer arranged above it, which can also be made from silicon nitride. This anti-migration layer should compensate for the diffusion processes that lead to colour shifts during and after the thermal treatment. However, practical trials have shown that this only works in certain thermal treatment processes.
A further possibility to avoid colour variations in adjacent, thermally treated and non-heat treated glass is described in EP 0646 551. According to this, along with the mechanical and chemical characteristics, the optical characteristics of the layer system in particular are precisely set with the use of a further silicon nitride layer below the infrared-reflecting metal layer as well as variable thicknesses of one or both silicon nitride coatings as a result of which specific, minimal colour differentiations can be created so that after the thermal treatment, no visible colour differences remain and this coated glass can be used in one facade. However, for this process, two different layer systems that are precisely compatible with each other and the thermal treatment must be manufactured. This matching of the coating systems is necessary for every colour to be used and therefore very cost-intensive and inflexible as well as only possible insofar as the required mechanical and chemical durability of the respective layer system permits.
The use of different, matching layer systems in an application can only be avoided through layer systems that do not significantly change their optical characteristics even during such thermal treatments in which, in terms of length and treatment temperatures, the usual ranges within the various processes can be fully utilised and both parameters can be flexibly selected at the same time. To this end, a layer system is described in U.S. Pat. No. 6,524,714 in which, instead of the known nickel-containing reflective layer, an at least partially nitrided metal layer is used, preferably a nickel-or chrome-containing metal nitride. The level of nitridation of the metal is regulated through the nitrogen portion in the working gas of the coating section on which the metal is applied.
Through the nitridation of the reflecting metal layer, the described diffusion processes in the layer system, particularly of the nitrogen, and therefore its colour shifts, are reduced at least in the framework of the described thermal treatments of 10 minutes at 625° C. A layer system with the same but nitride-free metal layer and that has undergone the same thermal treatment serves as a comparison.
However, the nitridation of the metal is linked with a decrease in reflective properties, particularly in the infrared range, as well as a reduction in mechanical and chemical durability. The reduced durability can be balanced out through a modification of the silicon nitride layers. However, this is then in every case linked to a change in the optical properties so that a compromise must be found between colour shifts and durability.
Furthermore, it is necessary to subject such a reflective layer system to more flexible thermal treatment processes and in this way meet the requirements in terms of mechanical, chemical and optical properties. This is why the invention has the task of portraying a layer system that filters sun and can be applied to glass by means of a vacuum coating process, and a method for producing the same that can be variably thermally treated and that, while maintaining chemical and mechanical durability, does not evince any visible colour shift.